Positional and geometrical isomerization during partial hydrogenation of trilinolein: A comparison of copper and nickel catalysts

We have compared a nickel with a copper catalyst in the formation of some geometrical and positional isomers during the partial hydrogenation of trilinolein. The copper catalyst was found to produce fewer diene isomers than the nickel catalyst at a comparable iodine value. The copper catalyst produced more monoene isomers however, than did the nickel, particularlytrans monoenes. The distribution of the monoene isomers appeared to obey an equilibrium relationship with each other, independent of both iodine value and reaction conditions. We have presented additional evidence to postulate that copper catalysts hydrogenate polyenoic acids by first conjugating the acids. The selectivity of copper catalysts for triene over diene is probably due to the greater ease of conjugation of the triene.